1) Open chrome with a profile that's not signed in
2) Go to chrome://settings/syncSetup
3) Login to Chrome, and click to "more options in settings"

Expected:
Sync is not supposed to start yet (you can see this by going to chrome://settings in a new tab, and the sync row should say "setup in progress..."

Actual: 
Sync actually starts (you can see this by observing that your extensions, bookmarks etc are already being loaded in, as well as going to chrome://settings and see "on - everything is synced" in the sync row.)